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Full text of "Text Book Of Mechanical Engineering"

Fly-wheel Moulding.                           27

from it may reach quite round the outer rim of the wheel, as suggested
by the dotted lines; the back and top boards B and c being loose, to
remove the core, which may be made in dry sand. After levelling the
floor by means of board D, Fig. 39, the cores from Fig. 40 are set up
at E, with the curved surface inward and gauged from the centre by
the striking board F, which has the same radius as the outside of the
fly-wheel rim. A small space is, however, left for the application of a
coating of loam which is struck out at top and side by the board F.

We next require the arm cores. The box for these is shewn at
Fig. 41, and supposing we have in our case six arms to the wheel
this box must be made a sector of one-sixth part of the circle.
The top, bottom, and sides are removable, so that when the
box has been filled with compact ' dry sand' they may be taken
away, together with the rim part and boss, leaving the arm, which,
being tapered, may be knocked out with a mallet at G and so
removed. Some moulders might prefer loam for these cores,
which would be baked in the usual way.

Putting the sector cores in place, as in Fig. 42, a pattern is
used for the boss, with a cope of green sand at H. There only
remains the completion of the cope for the rim. This may .be
done in dry sand, contained in boxes shown in plan at j, and by
means of a pattern K placed in the channel formed for the rim,
top box j being put on and rammed up there. This pattern K is
passed round until the whole of the top of the rim is formed, and
is finally withdrawn by removing one of the boxes. The mould is
now complete, and it is only necessary to form the gates, which
should be pretty central, while risers (about four) are put in the
boxes j to shew when the metal has filled the rim, which is known
by its lifting a metal ball placed upon them. Of course great care
must be taken in finishing the mould, so that no unsightly marks
be left on the casting at places where the cores join each other.

Marine Condensers, being usually large cubical castings, are
built up in loam in the manner described for other objects, by the
aid of what are known as skeleton patterns, projecting flanges
having patterns and core boxes. (See Appendix //,,/. 782.)

Fig. 43 shews one or two objects suitable for loam moulding,
A being a large Air Vessel for a pump, and B a Cone Pulley
for some machine tool